Remember the following rule:
-=over 5
+=over 8
-=item *
+=item
I<THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR!>
operations. In general, they do what you want, unless you want
consistency.
+=head2 Perl Functions by Category
+
+Here are Perl's functions (including things that look like
+functions, like some of the keywords and named operators)
+arranged by category. Some functions appear in more
+than one place.
+
+=over
+
+=item Functions for SCALARs or strings
+
+chomp, chop, chr, crypt, hex, index, lc, lcfirst, length,
+oct, ord, pack, q/STRING/, qq/STRING/, reverse, rindex,
+sprintf, substr, tr///, uc, ucfirst, y///
+
+=item Regular expressions and pattern matching
+
+m//, pos, quotemeta, s///, split, study
+
+=item Numeric functions
+
+abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt,
+srand
+
+=item Functions for real @ARRAYs
+
+pop, push, shift, splice, unshift
+
+=item Functions for list data
+
+grep, join, map, qw/STRING/, reverse, sort, unpack
+
+=item Functions for real %HASHes
+
+delete, each, exists, keys, values
+
+=item Input and output functions
+
+binmode, close, closedir, dbmclose, dbmopen, die, eof,
+fileno, flock, format, getc, print, printf, read, readdir,
+rewinddir, seek, seekdir, select, syscall, sysread,
+syswrite, tell, telldir, truncate, warn, write
+
+=item Functions for fixed length data or records
+
+pack, read, syscall, sysread, syswrite, unpack, vec
+
+=item Functions for filehandles, files, or directories
+
+I<-X>, chdir, chmod, chown, chroot, fcntl, glob, ioctl, link,
+lstat, mkdir, open, opendir, readlink, rename, rmdir,
+stat, symlink, umask, unlink, utime
+
+=item Keywords related to the control flow of your perl program
+
+caller, continue, die, do, dump, eval, exit, goto, last,
+next, redo, return, sub, wantarray
+
+=item Keywords related to scoping
+
+caller, import, local, my, package, use
+
+=item Miscellaneous functions
+
+defined, dump, eval, formline, local, my, reset, scalar,
+undef, wantarray
+
+=item Functions for processes and process groups
+
+alarm, exec, fork, getpgrp, getppid, getpriority, kill,
+pipe, qx/STRING/, setpgrp, setpriority, sleep, system,
+times, wait, waitpid
+
+=item Keywords related to perl modules
+
+do, import, no, package, require, use
+
+=item Keywords related to classes and object-orientedness
+
+bless, dbmclose, dbmopen, package, ref, tie, tied, untie, use
+
+=item Low-level socket functions
+
+accept, bind, connect, getpeername, getsockname,
+getsockopt, listen, recv, send, setsockopt, shutdown,
+socket, socketpair
+
+=item System V interprocess communication functions
+
+msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop,
+shmctl, shmget, shmread, shmwrite
+
+=item Fetching user and group info
+
+endgrent, endhostent, endnetent, endpwent, getgrent,
+getgrgid, getgrnam, getlogin, getpwent, getpwnam,
+getpwuid, setgrent, setpwent
+
+=item Fetching network info
+
+endprotoent, endservent, gethostbyaddr, gethostbyname,
+gethostent, getnetbyaddr, getnetbyname, getnetent,
+getprotobyname, getprotobynumber, getprotoent,
+getservbyname, getservbyport, getservent, sethostent,
+setnetent, setprotoent, setservent
+
+=item Time-related functions
+
+gmtime, localtime, time, times
+
+=item Functions new in perl5
+
+abs, bless, chomp, chr, exists, formline, glob, import, lc,
+lcfirst, map, my, no, prototype, qx, qw, readline, readpipe,
+ref, sub*, sysopen, tie, tied, uc, ucfirst, untie, use
+
+* - C<sub> was a keyword in perl4, but in perl5 it is an
+operator which can be used in expressions.
+
+=item Functions obsoleted in perl5
+
+dbmclose, dbmopen
+
+
+=back
+
+=head2 Alphabetical Listing of Perl Functions
+
+
=over 8
=item -X FILEHANDLE
=item binmode FILEHANDLE
-Arranges for the file to be read or written in "binary" mode in
-operating systems that distinguish between binary and text files.
-Files that are not in binary mode have CR LF sequences translated to LF
-on input and LF translated to CR LF on output. Binmode has no effect
-under Unix; in DOS, it may be imperative--otherwise your DOS C library
-may mangle your file. If FILEHANDLE is an expression,
-the value is taken as the name of the filehandle.
+Arranges for the file to be read or written in "binary" mode in operating
+systems that distinguish between binary and text files. Files that are
+not in binary mode have CR LF sequences translated to LF on input and LF
+translated to CR LF on output. Binmode has no effect under Unix; in DOS
+and similarly archaic systems, it may be imperative--otherwise your
+DOS-damaged C library may mangle your file. The key distinction between
+systems that need binmode and those that don't is their text file
+formats. Systems like Unix and Plan9 that delimit lines with a single
+character, and that encode that character in C as '\n', do not need
+C<binmode>. The rest need it. If FILEHANDLE is an expression, the value
+is taken as the name of the filehandle.
=item bless REF,CLASSNAME
packed address of the appropriate type for the socket. See the examples in
L<perlipc/"Sockets: Client/Server Communication">.
+=item continue BLOCK
+
+Actually a flow control statement rather than a function. If there is a
+C<continue> BLOCK attached to a BLOCK (typically in a C<while> or
+C<foreach>), it is always executed just before the conditional is about to
+be evaluated again, just like the third part of a C<for> loop in C. Thus
+it can be used to increment a loop variable, even when the loop has been
+continued via the C<next> statement (which is similar to the C C<continue>
+statement).
+
=item cos EXPR
Returns the cosine of EXPR (expressed in radians). If EXPR is omitted
[This function has been superseded by the tie() function.]
-This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to an associative array. ASSOC is the
-name of the associative array. (Unlike normal open, the first argument
-is I<NOT> a filehandle, even though it looks like one). DBNAME is the
-name of the database (without the F<.dir> or F<.pag> extension if any). If the
-database does not exist, it is created with protection specified by
-MODE (as modified by the umask()). If your system only supports the
-older DBM functions, you may perform only one dbmopen() in your program.
-In order versions of Perl,
-if your system had neither DBM nor ndbm, calling dbmopen() produced a
-fatal error; it now falls back to sdbm(3).
+This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to an
+associative array. ASSOC is the name of the associative array. (Unlike
+normal open, the first argument is I<NOT> a filehandle, even though it
+looks like one). DBNAME is the name of the database (without the F<.dir>
+or F<.pag> extension if any). If the database does not exist, it is
+created with protection specified by MODE (as modified by the umask()).
+If your system only supports the older DBM functions, you may perform only
+one dbmopen() in your program. In older versions of Perl, if your system
+had neither DBM nor ndbm, calling dbmopen() produced a fatal error; it now
+falls back to sdbm(3).
If you don't have write access to the DBM file, you can only read
associative array variables, not set them. If you want to test whether
}
dbmclose(%HIST);
-See also L<DB_File> for many other interesting possibilities.
+See also L<AnyDBM_File> for a more general description of the pros and
+cons of the various dbm apparoches, as well as L<DB_File> for a particularly
+rich implementation.
=item defined EXPR
-Returns a boolean value saying whether the lvalue EXPR has a real value
+Returns a boolean value saying whether EXPR has a real value
or not. Many operations return the undefined value under exceptional
conditions, such as end of file, uninitialized variable, system error
and such. This function allows you to distinguish between an undefined
See also undef().
+Note: many folks tend to overuse defined(), and then are surprised to
+discover that the number 0 and the null string are, in fact, defined
+concepts. For example, if you say
+
+ "ab" =~ /a(.*)b/;
+
+the pattern match succeeds, and $1 is defined, despite the fact that it
+matched "nothing". But it didn't really match nothing--rather, it
+matched something that happened to be 0 characters long. This is all
+very above-board and honest. When a function returns an undefined value,
+it's an admission that it couldn't give you an honest answer. So
+you should only use defined() when you're questioning the integrity
+of what you're trying to do. At other times, a simple comparison to
+0 or "" is what you want.
+
=item delete EXPR
Deletes the specified value from its hash array. Returns the deleted
=item each ASSOC_ARRAY
-Returns a 2-element array consisting of the key and value for the next
-value of an associative array, so that you can iterate over it.
+When called in a list context, returns a 2-element array consisting
+of the key and value for the next element of an associative array,
+so that you can iterate over it. When called in a scalar context,
+returns the key only for the next element in the associative array.
Entries are returned in an apparently random order. When the array is
-entirely read, a null array is returned (which when assigned produces a
-FALSE (0) value). The next call to each() after that will start
+entirely read, a null array is returned in list context (which when
+assigned produces a FALSE (0) value), and C<undef> is returned in a
+scalar context. The next call to each() after that will start
iterating again. The iterator can be reset only by reading all the
elements from the array. You should not add elements to an array while
you're iterating over it. There is a single iterator for each
An C<eof> without an argument uses the last file read as argument.
Empty parentheses () may be used to indicate
the pseudofile formed of the files listed on the command line, i.e.
-C<eof()> is reasonable to use inside a while (<>) loop to detect the end
+C<eof()> is reasonable to use inside a while (E<lt>E<gt>) loop to detect the end
of only the last file. Use C<eof(ARGV)> or eof without the parentheses to
-test I<EACH> file in a while (<>) loop. Examples:
+test I<EACH> file in a while (E<lt>E<gt>) loop. Examples:
# reset line numbering on each input file
while (<>) {
}
Practical hint: you almost never need to use C<eof> in Perl, because the
-input operators return undef when they run out of data. Testing C<eof>
+input operators return undef when they run out of data.
=item eval EXPR
likewise behave in the same way: they run the code <$x>, which does
nothing at all. (Case 4 is preferred for purely visual reasons.) Case 5
is a place where normally you I<WOULD> like to use double quotes, except
-in that particular situation, you can just use symbolic references
+that in that particular situation, you can just use symbolic references
instead, as in case 6.
=item exec LIST
metacharacters. If there are any, the entire argument is passed to
C</bin/sh -c> for parsing. If there are none, the argument is split
into words and passed directly to execvp(), which is more efficient.
-Note: exec() (and system(0) do not flush your output buffer, so you may
+Note: exec() and system() do not flush your output buffer, so you may
need to set C<$|> to avoid lost output. Examples:
exec '/bin/echo', 'Your arguments are: ', @ARGV;
Calls flock(2) on FILEHANDLE. See L<flock(2)> for definition of
OPERATION. Returns TRUE for success, FALSE on failure. Will produce a
fatal error if used on a machine that doesn't implement either flock(2) or
-fcntl(2). (fcntl(2) will be automatically used if flock(2) is missing.)
+fcntl(2). The fcntl(2) system call will be automatically used if flock(2)
+is missing from your system. This makes flock() the portable file locking
+strategy, although it will only lock entire files, not records. Note also
+that some versions of flock() cannot lock things over the network; you
+would need to use the more system-specific fcntl() for that.
Here's a mailbox appender for BSD systems.
print MBOX $msg,"\n\n";
unlock();
-Note that many versions of flock() cannot lock things over the network.
-You need to do locking with fcntl() for that.
+See also L<DB_File> for other flock() examples.
=item fork
}
waitpid($pid,0);
+See also L<perlipc> for more examples of forking and reaping
+moribund children.
+
+=item format
+
+Declare a picture format with use by the write() function. For
+example:
+
+ format Something =
+ Test: @<<<<<<<< @||||| @>>>>>
+ $str, $%, '$' . int($num)
+ .
+
+ $str = "widget";
+ $num = $cost/$quantiy;
+ $~ = 'Something';
+ write;
+
+See L<perlform> for many details and examples.
+
=item formline PICTURE, LIST
Returns the next character from the input file attached to FILEHANDLE,
or a null string at end of file. If FILEHANDLE is omitted, reads from STDIN.
This is not particularly efficient. It cannot be used to get unbuffered
-single-character
+single-characters, however. For that, try something more like:
if ($BSD_STYLE) {
system "stty cbreak </dev/tty >/dev/tty 2>&1";
}
else {
- system "stty", '-icanon',
- system "stty", 'eol', "\001";
+ system "stty", '-icanon', 'eol', "\001";
}
$key = getc(STDIN);
system "stty -cbreak </dev/tty >/dev/tty 2>&1";
}
else {
- system "stty", 'icanon';
- system "stty", 'eol', '^@'; # ascii null
+ system "stty", 'icanon', 'eol', '^@'; # ascii null
}
print "\n";
Determination of whether to whether $BSD_STYLE should be set
-is left as an exercise to the reader.
+is left as an exercise to the reader.
+
+See also the C<Term::ReadKey> module from your nearest CPAN site;
+details on CPAN can be found on L<perlmod/CPAN>
=item getlogin
$login = getlogin || (getpwuid($<))[0] || "Kilroy";
-Do not consider getlogin() for authorentication: it is not as
+Do not consider getlogin() for authentication: it is not as
secure as getpwuid().
=item getpeername SOCKET
}
To sort an array by value, you'll need to use a C<sort{}>
-function. Here's a descending numeric sort by value:
+function. Here's a descending numeric sort of a hash by its values:
foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash)) {
printf "%4d %s\n", $hash{$key}, $key;
process groups instead of processes. (On System V, a negative I<PROCESS>
number will also kill process groups, but that's not portable.) That
means you usually want to use positive not negative signals. You may also
-use a signal name in quotes. See the L<perlipc/"Signals"> man page for details.
+use a signal name in quotes. See L<perlipc/"Signals"> for details.
=item last LABEL
=item local EXPR
-In general, you should be using "my" instead of "local", because it's
-faster and safer. Format variables often use "local" though, as
-do other variables whose current value must be visible to called
-subroutines. This is known as dynamic scoping. Lexical scoping is
-done with "my", which works more like C's auto declarations.
-
A local modifies the listed variables to be local to the enclosing block,
-subroutine, eval or "do". If more than one value is listed, the list
-must be placed in parens. All the listed elements must be legal
-lvalues. This operator works by saving the current values of those
-variables in LIST on a hidden stack and restoring them upon exiting the
-block, subroutine or eval. This means that called subroutines can also
-reference the local variable, but not the global one. The LIST may be
-assigned to if desired, which allows you to initialize your local
-variables. (If no initializer is given for a particular variable, it
-is created with an undefined value.) Commonly this is used to name the
-parameters to a subroutine. Examples:
-
- sub RANGEVAL {
- local($min, $max, $thunk) = @_;
- local $result = '';
- local $i;
-
- # Presumably $thunk makes reference to $i
-
- for ($i = $min; $i < $max; $i++) {
- $result .= eval $thunk;
- }
+subroutine, C<eval{}> or C<do>. If more than one value is listed, the
+list must be placed in parens. See L<perlsub/"Temporary Values via
+local()"> for details.
- $result;
- }
-
-
- if ($sw eq '-v') {
- # init local array with global array
- local @ARGV = @ARGV;
- unshift(@ARGV,'echo');
- system @ARGV;
- }
- # @ARGV restored
-
-
- # temporarily add to digits associative array
- if ($base12) {
- # (NOTE: not claiming this is efficient!)
- local(%digits) = (%digits,'t',10,'e',11);
- parse_num();
- }
-
-Note that local() is a run-time command, and so gets executed every
-time through a loop. In Perl 4 it used more stack storage each
-time until the loop was exited. Perl 5 reclaims the space each time
-through, but it's still more efficient to declare your variables
-outside the loop.
-
-A local is simply a modifier on an lvalue expression.
-When you assign to a localized EXPR, the local doesn't change whether
-EXPR is viewed as a scalar or an array. So
-
- local($foo) = <STDIN>;
- local @FOO = <STDIN>;
-
-both supply a list context to the righthand side, while
-
- local $foo = <STDIN>;
-
-supplies a scalar context.
+But you really probably want to be using my() instead, because local() isn't
+what most people think of as "local"). See L<perlsub/"Private Variables
+via my()"> for details.
=item localtime EXPR
$now_string = localtime; # e.g. "Thu Oct 13 04:54:34 1994"
-See also L<perlmod/timelocal> and the strftime(3) function available
-via the POSIX modulie.
+Also see the F<timelocal.pl> library, and the strftime(3) function available
+via the POSIX module.
=item log EXPR
Calls the System V IPC function msgsnd to send the message MSG to the
message queue ID. MSG must begin with the long integer message type,
-which may be created with C<pack("L", $type)>. Returns TRUE if
+which may be created with C<pack("l", $type)>. Returns TRUE if
successful, or FALSE if there is an error.
=item msgrcv ID,VAR,SIZE,TYPE,FLAGS
=item my EXPR
A "my" declares the listed variables to be local (lexically) to the
-enclosing block, subroutine, C<eval>, or C<do/require/use>'d file. If more than one value is
-listed, the list must be placed in parens. All the listed elements
-must be legal lvalues. Only alphanumeric identifiers may be lexically
-scoped--magical builtins like $/ must be localized with "local"
-instead. You also cannot use my() on a package variable.
-In particular, you're not allowed to say
-
- my $_; # Illegal!
- my $pack::$var; # Illegal!
-
-Unlike the "local" declaration, variables declared with "my"
-are totally hidden from the outside world, including any called
-subroutines (even if it's the same subroutine--every call gets its own
-copy).
-
-(An eval(), however, can see the lexical variables of the scope it is
-being evaluated in so long as the names aren't hidden by declarations within
-the eval() itself. See L<perlref>.)
-
-The EXPR may be assigned to if desired, which allows you to initialize
-your variables. (If no initializer is given for a particular
-variable, it is created with an undefined value.) Commonly this is
-used to name the parameters to a subroutine. Examples:
-
- sub RANGEVAL {
- my($min, $max, $thunk) = @_;
- my $result = '';
- my $i;
-
- # Presumably $thunk makes reference to $i
-
- for ($i = $min; $i < $max; $i++) {
- $result .= eval $thunk;
- }
-
- $result;
- }
-
-
- if ($sw eq '-v') {
- # init my array with global array
- my @ARGV = @ARGV;
- unshift(@ARGV,'echo');
- system @ARGV;
- }
- # Outer @ARGV again visible
-
-The "my" is simply a modifier on something you might assign to.
-So when you do assign to the EXPR, the "my" doesn't change whether
-EXPR is viewed as a scalar or an array. So
-
- my ($foo) = <STDIN>;
- my @FOO = <STDIN>;
-
-both supply a list context to the righthand side, while
-
- my $foo = <STDIN>;
-
-supplies a scalar context. But the following only declares one variable:
-
- my $foo, $bar = 1;
-
-That has the same effect as
-
- my $foo;
- $bar = 1;
-
-The declared variable is not introduced (is not visible) until after
-the current statement. Thus,
-
- my $x = $x;
-
-can be used to initialize the new $x with the value of the old $x, and
-the expression
-
- my $x = 123 and $x == 123
-
-is false unless the old $x happened to have the value 123.
-
-Some users may wish to encourage the use of lexically scoped variables.
-As an aid to catching implicit references to package variables,
-if you say
-
- use strict 'vars';
-
-then any variable reference from there to the end of the enclosing
-block must either refer to a lexical variable, or must be fully
-qualified with the package name. A compilation error results
-otherwise. An inner block may countermand this with S<"no strict 'vars'">.
-
-Variables declared with "my" are not part of any package and
-are therefore never fully qualified with the package name.
-However, you may declare a "my" variable at the outer most
-scope of a file to totally hide any such identifiers from the
-outside world. This is similar to a C's static variables
-at the file level. To do this with a subroutine requires the
-use of a closure (anonymous function):
-
- my $secret_version = '1.001-beta';
- my $secret_sub = { print $secret_version };
- &$secret_sub();
-
-This does not work with object methods, however;
-all object methods have to be in the symbol table of some
-package to be found.
-
-Just because the "my" variable is lexically scoped doesn't mean that
-within a function it works like a C static. Here's a mechanism for giving
-a function private variables with both lexical scoping and a static
-lifetime.
-
- #!/usr/bin/perl -l
- $var = "global";
- { my $count = 0;
- my $var = "static";
- sub foo {
- $count++;
- print "$var (call # $count)";
- }
- }
- print $var; foo();
- print $var; foo();
- print $var; foo();
+enclosing block, subroutine, C<eval>, or C<do/require/use>'d file. If
+more than one value is listed, the list must be placed in parens. See
+L<perlsub/"Private Variables via my()"> for details.
=item next LABEL
the same name as the FILEHANDLE contains the filename. If the filename
begins with "<" or nothing, the file is opened for input. If the filename
begins with ">", the file is opened for output. If the filename begins
-with ">>", the file is opened for appending. (You can put a '+' in front
+with ">>", the file is opened for appending. You can put a '+' in front
of the '>' or '<' to indicate that you want both read and write access to
-the file.) If the filename begins with "|", the filename is interpreted
+the file; thus '+<' is usually preferred for read/write updates--the '+>'
+mode would clobber the file first. These correspond to the fopen(3) modes
+of 'r', 'r+', 'w', 'w+', 'a', and 'a+'.
+
+If the filename begins with "|", the filename is interpreted
as a command to which output is to be piped, and if the filename ends with
a "|", the filename is interpreted See L<perlipc/"Using open() for IPC">
for more examples of this. as command which pipes input to us. (You may
-not have a command that pipes both in and out, but see See L<open2>,
+not have a raw open() to a command that pipes both in I<and> out, but see L<open2>,
L<open3>, and L<perlipc/"Bidirectional Communication"> for alternatives.)
+
Opening '-' opens STDIN and opening '>-' opens STDOUT. Open returns
non-zero upon success, the undefined value otherwise. If the open
involved a pipe, the return value happens to be the pid of the
-subprocess. Examples:
+subprocess.
+
+If you're unfortunate enough to be running Perl on a system that
+distinguishes between text files and binary files (modern operating
+systems don't care), then you should check out L</binmode> for tips for
+dealing with this. The key distinction between systems that need binmode
+and those that don't is their text file formats. Systems like Unix and
+Plan9 that delimit lines with a single character, and that encode that
+character in C as '\n', do not need C<binmode>. The rest need it.
+
+Examples:
$ARTICLE = 100;
open ARTICLE or die "Can't find article $ARTICLE: $!\n";
open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved)
+ open(DBASE, '+<dbase.mine'); # open for update
+
open(ARTICLE, "caesar <$article |"); # decrypt article
open(EXTRACT, "|sort >/tmp/Tmp$$"); # $$ is our process id
name of a filehandle (or file descriptor, if numeric) which is to be
duped and opened. You may use & after >, >>, <, +>, +>> and +<. The
mode you specify should match the mode of the original filehandle.
+(Duping a filehandle does not take into acount any existing contents of
+stdio buffers.)
Here is a script that saves, redirects, and restores STDOUT and
STDERR:
unflushed in both processes, which means you may need to set $| to
avoid duplicate output.
+Using the FileHandle constructor from the FileHandle package,
+you can generate anonymous filehandles which have the scope of whatever
+variables hold references to them, and automatically close whenever
+and however you leave that scope:
+
+ use FileHandle;
+ ...
+ sub read_myfile_munged {
+ my $ALL = shift;
+ my $handle = new FileHandle;
+ open($handle, "myfile") or die "myfile: $!";
+ $first = <$handle>
+ or return (); # Automatically closed here.
+ mung $first or die "mung failed"; # Or here.
+ return $first, <$handle> if $ALL; # Or here.
+ $first; # Or here.
+ }
+
The filename that is passed to open will have leading and trailing
whitespace deleted. In order to open a file with arbitrary weird
characters in it, it's necessary to protect any leading and trailing
whitespace thusly:
- $file =~ s#^(\s)#./$1#;
- open(FOO, "< $file\0");
+ $file =~ s#^(\s)#./$1#;
+ open(FOO, "< $file\0");
+
+If you want a "real" C open() (see L<open(2)> on your system), then
+you should use the sysopen() function. This is another way to
+protect your filenames from interpretation. For example:
+
+ use FileHandle;
+ sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL, 0700)
+ or die "sysopen $path: $!";
+ HANDLE->autoflush(1);
+ HANDLE->print("stuff $$\n");
+ seek(HANDLE, 0, 0);
+ print "File contains: ", <HANDLE>;
+
+See L</seek()> for some details about mixing reading and writing.
=item opendir DIRHANDLE,EXPR
The same template may generally also be used in the unpack function.
+=item package NAMESPACE
+
+Declares the compilation unit as being in the given namespace. The scope
+of the package declaration is from the declaration itself through the end of
+the enclosing block (the same scope as the local() operator). All further
+unqualified dynamic identifiers will be in this namespace. A package
+statement only affects dynamic variables--including those you've used
+local() on--but I<not> lexical variables created with my(). Typically it
+would be the first declaration in a file to be included by the C<require>
+or C<use> operator. You can switch into a package in more than one place;
+it merely influences which symbol table is used by the compiler for the
+rest of that block. You can refer to variables and filehandles in other
+packages by prefixing the identifier with the package name and a double
+colon: C<$Package::Variable>. If the package name is null, the C<main>
+package as assumed. That is, C<$::sail> is equivalent to C<$main::sail>.
+
+See L<perlmod/"Packages"> for more information about packages, modules,
+and classes. See L<perlsub> for other scoping issues.
+
=item pipe READHANDLE,WRITEHANDLE
Opens a pair of connected pipes like the corresponding system call.
$tmp = $ARRAY[$#ARRAY--];
If there are no elements in the array, returns the undefined value.
+If ARRAY is omitted, pops the
+@ARGV array in the main program, and the @_ array in subroutines, just
+like shift().
=item pos SCALAR
=item print
-Prints a string or a comma-separated list of strings. Returns non-zero
+Prints a string or a comma-separated list of strings. Returns TRUE
if successful. FILEHANDLE may be a scalar variable name, in which case
-the variable contains the name of the filehandle, thus introducing one
+the variable contains the name of or a reference to the filehandle, thus introducing one
level of indirection. (NOTE: If FILEHANDLE is a variable and the next
token is a term, it may be misinterpreted as an operator unless you
interpose a + or put parens around the arguments.) If FILEHANDLE is
omitted, prints by default to standard output (or to the last selected
-output channel--see select()). If LIST is also omitted, prints $_ to
+output channel--see L</select>). If LIST is also omitted, prints $_ to
STDOUT. To set the default output channel to something other than
STDOUT use the select operation. Note that, because print takes a
LIST, anything in the LIST is evaluated in a list context, and any
put parens around all the arguments.
Note that if you're storing FILEHANDLES in an array or other expression,
-you will have to use a block returning its value instead
+you will have to use a block returning its value instead:
print { $files[$i] } "stuff\n";
print { $OK ? STDOUT : STDERR } "stuff\n";
Equivalent to a "print FILEHANDLE sprintf(LIST)". The first argument
of the list will be interpreted as the printf format.
+=item prototype FUNCTION
+
+Returns the prototype of a function as a string (or C<undef> if the
+function has no prototype). FUNCTION is a reference to the the
+function whose prototype you want to retrieve.
+
=item push ARRAY,LIST
Treats ARRAY as a stack, and pushes the values of LIST
directory. If there are no more entries, returns an undefined value in
a scalar context or a null list in a list context.
+If you're planning to filetest the return values out of a readdir(), you'd
+better prepend the directory in question. Otherwise, since we didn't
+chdir() there, it would have been testing the wrong file.
+
+ opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
+ @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
+ closedir DIR;
+
=item readlink EXPR
Returns the value of a symbolic link, if symbolic links are
otherwise. But it's better just to put the "C<1;>", in case you add more
statements.
-If EXPR is a bare word, the require assumes a "F<.pm>" extension for you,
+If EXPR is a bare word, the require assumes a "F<.pm>" extension and
+replaces "F<::>" with "F</>" in the filename for you,
to make it easy to load standard modules. This form of loading of
modules does not risk altering your namespace.
-For a yet-more-powerful import facility, see the L</use()> and
+For a yet-more-powerful import facility, see L</use> and
L<perlmod>.
=item reset EXPR
Resetting "A-Z" is not recommended since you'll wipe out your
ARGV and ENV arrays. Only resets package variables--lexical variables
are unaffected, but they clean themselves up on scope exit anyway,
-so anymore you probably want to use them instead. See L</my>.
+so you'll probably want to use them instead. See L</my>.
=item return LIST
=item scalar EXPR
Forces EXPR to be interpreted in a scalar context and returns the value
-of EXPR.
+of EXPR.
+
+ @counts = ( scalar @a, scalar @b, scalar @c );
+
+There is no equivalent operator to force an expression to
+be interpolated in a list context because it's in practice never
+needed. If you really wanted to do so, however, you could use
+the construction C<@{[ (some expression) ]}>, but usually a simple
+C<(some expression)> suffices.
=item seek FILEHANDLE,POSITION,WHENCE
plus offset. You may use the values SEEK_SET, SEEK_CUR, and SEEK_END for
this from POSIX module. Returns 1 upon success, 0 otherwise.
+On some systems you have to do a seek whenever you switch between reading
+and writing. Amongst other things, this may have the effect of calling
+stdio's clearerr(3). A "whence" of 1 (SEEK_CUR) is useful for not moving
+the file pointer:
+
+ seek(TEST,0,1);
+
+This is also useful for applications emulating C<tail -f>. Once you hit
+EOF on your read, and then sleep for a while, you might have to stick in a
+seek() to reset things. First the simple trick listed above to clear the
+filepointer. The seek() doesn't change the current position, but it
+I<does> clear the end-of-file condition on the handle, so that the next
+C<E<lt>FILEE<gt>> makes Perl try again to read something. Hopefully.
+
+If that doesn't work (some stdios are particularly cantankerous), then
+you may need something more like this:
+
+ for (;;) {
+ for ($curpos = tell(FILE); $_ = <FILE>; $curpos = tell(FILE)) {
+ # search for some stuff and put it into files
+ }
+ sleep($for_a_while);
+ seek(FILE, $curpos, 0);
+ }
+
=item seekdir DIRHANDLE,POS
Sets the current position for the readdir() routine on DIRHANDLE. POS
($nfound,$timeleft) =
select($rout=$rin, $wout=$win, $eout=$ein, $timeout);
-or to block until something becomes ready:
+or to block until something becomes ready just do this
$nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);
+Most systems do not both to return anything useful in $timeleft, so
+calling select() in a scalar context just returns $nfound.
+
Any of the bitmasks can also be undef. The timeout, if specified, is
in seconds, which may be fractional. Note: not all implementations are
capable of returning the $timeleft. If not, they always return
$timeleft equal to the supplied $timeout.
-You can effect a 250-microsecond sleep this way:
+You can effect a 250-millisecond sleep this way:
select(undef, undef, undef, 0.25);
+B<WARNING>: Do not attempt to mix buffered I/O (like read() or <FH>)
+with select(). You have to use sysread() instead.
=item semctl ID,SEMNUM,CMD,ARG
you requested, depending on how it counts seconds. Most modern systems
always sleep the full amount.
+For delays of finer granularity than one second, you may use Perl's
+syscall() interface to access setitimer(2) if your system supports it,
+or else see L</select()> below.
+
=item socket SOCKET,DOMAIN,TYPE,PROTOCOL
Opens a socket of the specified kind and attaches it to filehandle
SUBNAME, you can provide a BLOCK as an anonymous, in-line sort
subroutine.
-In the interests of efficiency the normal calling code for subroutines
-is bypassed, with the following effects: the subroutine may not be a
-recursive subroutine, and the two elements to be compared are passed
-into the subroutine not via @_ but as $a and $b (see example below).
-They are passed by reference, so don't modify $a and $b.
+In the interests of efficiency the normal calling code for subroutines is
+bypassed, with the following effects: the subroutine may not be a
+recursive subroutine, and the two elements to be compared are passed into
+the subroutine not via @_ but as the package global variables $a and
+$b (see example below). They are passed by reference, so don't
+modify $a and $b. And don't try to declare them as lexicals either.
Examples:
# same thing, but with explicit sort routine
@articles = sort {$a cmp $b} @files;
+ # now case-insensitively
+ @articles = sort { uc($a) cmp uc($b)} @files;
+
# same thing in reversed order
@articles = sort {$b cmp $a} @files;
}
@sortedclass = sort byage @class;
+ # this sorts the %age associative arrays by value
+ # instead of key using an inline function
+ @eldest = sort { $age{$b} <=> $age{$a} } keys %age;
+
sub backwards { $b cmp $a; }
@harry = ('dog','cat','x','Cain','Abel');
@george = ('gone','chased','yz','Punished','Axed');
print sort @george, 'to', @harry;
# prints AbelAxedCainPunishedcatchaseddoggonetoxyz
+ # inefficiently sort by descending numeric compare using
+ # the first integer after the first = sign, or the
+ # whole record case-insensitively otherwise
+
+ @new = sort {
+ ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
+ ||
+ uc($a) cmp uc($b)
+ } @old;
+
+ # same thing, but much more efficiently;
+ # we'll build auxiliary indices instead
+ # for speed
+ @nums = @caps = ();
+ for (@old) {
+ push @nums, /=(\d+)/;
+ push @caps, uc($_);
+ }
+
+ @new = @old[ sort {
+ $nums[$b] <=> $nums[$a]
+ ||
+ $caps[$a] cmp $caps[$b]
+ } 0..$#old
+ ];
+
+ # same thing using a Schwartzian Transform (no temps)
+ @new = map { $_->[0] }
+ sort { $b->[1] <=> $a->[1]
+ ||
+ $a->[2] cmp $b->[2]
+ } map { [$_, /=(\d+)/, uc($_)] } @old;
+
+If you're and using strict, you I<MUST NOT> declare $a
+and $b as lexicals. They are package globals. That means
+if you're in the C<main> package, it's
+
+ @articles = sort {$main::b <=> $main::a} @files;
+
+or just
+
+ @articles = sort {$::b <=> $::a} @files;
+
+but if you're in the C<FooPack> package, it's
+
+ @articles = sort {$FooPack::b <=> $FooPack::a} @files;
+
=item splice ARRAY,OFFSET,LENGTH,LIST
=item splice ARRAY,OFFSET,LENGTH
If the PATTERN contains parentheses, additional array elements are
created from each matching substring in the delimiter.
- split(/([,-])/, "1-10,20");
+ split(/([,-])/, "1-10,20", 3);
produces the list value
=item sprintf FORMAT,LIST
Returns a string formatted by the usual printf conventions of the C
-language. (The * character for an indirectly specified length is not
+language. See L<sprintf(3)> or L<printf(3)> on your system for details.
+(The * character for an indirectly specified length is not
supported, but you can get the same effect by interpolating a variable
-into the pattern.) Some C libraries' implementations of sprintf() can dump core
-when fed ludiocrous arguments.
+into the pattern.) Some C libraries' implementations of sprintf() can
+dump core when fed ludicrous arguments.
=item sqrt EXPR
=item srand EXPR
-Sets the random number seed for the C<rand> operator. If EXPR is
-omitted, does C<srand(time)>. Of course, you'd need something much more
-random than that for cryptographic purposes, since it's easy to guess
-the current time. Checksumming the compressed output of rapidly
-changing operating system status programs is the usual method.
-Examples are posted regularly to comp.security.unix.
+Sets the random number seed for the C<rand> operator. If EXPR is omitted,
+uses a semirandom value based on the current time and process ID, among
+other things. Of course, you'd need something much more random than that for
+cryptographic purposes, since it's easy to guess the current time.
+Checksumming the compressed output of rapidly changing operating system
+status programs is the usual method. Examples are posted regularly to
+the comp.security.unix newsgroup.
=item stat FILEHANDLE
$atime,$mtime,$ctime,$blksize,$blocks)
= stat($filename);
+Not all fields are supported on all filesystem types. Here are the
+meaning of the fields:
+
+ dev device number of filesystem
+ ino inode number
+ mode file mode (type and permissions)
+ nlink number of (hard) links to the file
+ uid numeric user ID of file's owner
+ gid numer group ID of file's owner
+ rdev the device identifier (special files only)
+ size total size of file, in bytes
+ atime last access time since the epoch
+ mtime last modify time since the epoch
+ ctime inode change time (NOT creation type!) since the epoch
+ blksize preferred blocksize for file system I/O
+ blocks actual number of blocks allocated
+
+(The epoch was at 00:00 January 1, 1970 GMT.)
+
If stat is passed the special filehandle consisting of an underline, no
stat is done, but the current contents of the stat structure from the
last stat or filetest are returned. Example:
print $file, "\n";
}
+=item sub BLOCK
+
+=item sub NAME
+
+=item sub NAME BLOCK
+
+This is subroutine definition, not a real function I<per se>. With just a
+NAME (and possibly prototypes), it's just a forward declaration. Without
+a NAME, it's an anonymous function declaration, and does actually return a
+value: the CODE ref of the closure you just created. See L<perlsub> and
+L<perlref> for details.
+
=item substr EXPR,OFFSET,LEN
=item substr EXPR,OFFSET
Note that Perl only supports passing of up to 14 arguments to your system call,
which in practice should usually suffice.
+=item sysopen FILEHANDLE,FILENAME,MODE
+
+=item sysopen FILEHANDLE,FILENAME,MODE,PERMS
+
+Opens the file whose filename is given by FILENAME, and associates it
+with FILEHANDLE. If FILEHANDLE is an expression, its value is used as
+the name of the real filehandle wanted. This function calls the
+underlying operating system's C<open> function with the parameters
+FILENAME, MODE, PERMS.
+
+The possible values and flag bits of the MODE parameter are
+system-dependent; they are available via the standard module C<Fcntl>.
+However, for historical reasons, some values are universal: zero means
+read-only, one means write-only, and two means read/write.
+
+If the file named by FILENAME does not exist and the C<open> call
+creates it (typically because MODE includes the O_CREAT flag), then
+the value of PERMS specifies the permissions of the newly created
+file. If PERMS is omitted, the default value is 0666, which allows
+read and write for all. This default is reasonable: see C<umask>.
+
=item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
=item sysread FILEHANDLE,SCALAR,LENGTH
Note that argument processing varies depending on the number of
arguments. The return value is the exit status of the program as
returned by the wait() call. To get the actual exit value divide by
-256. See also L</exec>.
+256. See also L</exec>. This is I<NOT> what you want to use to capture
+the output from a command, for that you should merely use backticks, as
+described in L<perlop/"`STRING`">.
=item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
specified FILEHANDLE, using the system call write(2). It bypasses
stdio, so mixing this with prints may cause confusion. Returns the
number of bytes actually written, or undef if there was an error. An
-OFFSET may be specified to place the read data at some other place than
+OFFSET may be specified to get the write data from some other place than
the beginning of the string.
=item tell FILEHANDLE
of correct type. Any additional arguments are passed to the "new"
method of the class (meaning TIESCALAR, TIEARRAY, or TIEHASH).
Typically these are arguments such as might be passed to the dbm_open()
-function of C. The object returned by the "new" method +is also
-returned by the tie() function, which would be useful if you +want to
+function of C. The object returned by the "new" method is also
+returned by the tie() function, which would be useful if you want to
access other methods in CLASSNAME.
Note that functions such as keys() and values() may return huge array
# print out history file offsets
use NDBM_File;
- tie(%HIST, NDBM_File, '/usr/lib/news/history', 1, 0);
+ tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
while (($key,$val) = each %HIST) {
print $key, ' = ', unpack('L',$val), "\n";
}
for you--you need to do that explicitly yourself. See L<DB_File>
or the F<Config> module for interesting tie() implementations.
+=item tied VARIABLE
+
+Returns a reference to the object underlying VARIABLE (the same value
+that was originally returned by the tie() call which bound the variable
+to a package.) Returns the undefined value if VARIABLE isn't tied to a
+package.
+
=item time
-Returns the number of non-leap seconds since 00:00:00 UTC, January 1,
-1970. Suitable for feeding to gmtime() and localtime().
+Returns the number of non-leap seconds since whatever time the system
+considers to be the epoch (that's 00:00:00, January 1, 1904 for MacOS,
+and 00:00:00 UTC, January 1, 1970 for most other systems).
+Suitable for feeding to gmtime() and localtime().
=item times
=item use Module
+=item use Module VERSION LIST
+
+=item use VERSION
+
Imports some semantics into the current package from the named module,
generally by aliasing certain subroutine or variable names into your
package. It is exactly equivalent to
BEGIN { require Module; import Module LIST; }
-If you don't want your namespace altered, use require instead.
+except that Module I<must> be a bare word.
+
+If the first argument to C<use> is a number, it is treated as a version
+number instead of a module name. If the version of the Perl interpreter
+is less than VERSION, then an error message is printed and Perl exits
+immediately. This is often useful if you need to check the current
+Perl version before C<use>ing library modules which have changed in
+incompatible ways from older versions of Perl. (We try not to do
+this more than we have to.)
The BEGIN forces the require and import to happen at compile time. The
require makes sure the module is loaded into memory if it hasn't been
features back into the current package. The module can implement its
import method any way it likes, though most modules just choose to
derive their import method via inheritance from the Exporter class that
-is defined in the Exporter module.
+is defined in the Exporter module. See L<Exporter>.
+
+If you don't want your namespace altered, explicitly supply an empty list:
+
+ use Module ();
+
+That is exactly equivalent to
+
+ BEGIN { require Module; }
+
+If the VERSION argument is present between Module and LIST, then the
+C<use> will fail if the C<$VERSION> variable in package Module is
+less than VERSION.
Because this is a wide-open interface, pragmas (compiler directives)
are also implemented this way. Currently implemented pragmas are:
effective through the end of the file).
There's a corresponding "no" command that unimports meanings imported
-by use.
+by use, i.e. it calls C<unimport Module LIST> instead of C<import>.
no integer;
no strict 'refs';
associative array. (In a scalar context, returns the number of
values.) The values are returned in an apparently random order, but it
is the same order as either the keys() or each() function would produce
-on the same array. See also keys() and each().
+on the same array. See also keys(), each(), and sort().
=item vec EXPR,OFFSET,BITS
-Treats a string as a vector of unsigned integers, and returns the value
-of the bitfield specified. May also be assigned to. BITS must be a
-power of two from 1 to 32.
+Treats the string in EXPR as a vector of unsigned integers, and
+returns the value of the bitfield specified by OFFSET. BITS specifies
+the number of bits that are reserved for each entry in the bit
+vector. This must be a power of two from 1 to 32. vec() may also be
+assigned to, in which case parens are needed to give the expression
+the correct precedence as in
+
+ vec($image, $max_x * $x + $y, 8) = 3;
Vectors created with vec() can also be manipulated with the logical
operators |, & and ^, which will assume a bit vector operation is
=item y///
-The translation operator. See L<perlop/tr///>.
+The translation operator. See L<perlop>.
=back
projects / p5sagit/p5-mst-13.2.git / blobdiff